Energy mechanism of bolt supporting effect to fissured rock under static and dynamic loads in deep coal mines

The stability control of fissured rock is difficult, especially under static and dynamic loads in deep coal mines. In this paper, the dynamic mechanical properties, strain rate evolution and energy dissipation of fissured and anchored rocks were respectively obtained by SHPB tests. It was found that bolt can provide supporting efficiency-improving effect for fissured rock against dynamic disturbance, and this effect increased quadratically with decrease in anchoring angles. Then, the energy dissipation mechanism of anchored rock was obtained by slipping model. Furthermore, bolt energy-absorbing mechanism by instantaneous tensile-shear deformation was expressed based on material mechanics, which was the larger the anchoring angle, the smaller the energy absorption, and the less the contribution to supporting efficiency improvement. On this basis, the functional relationship between energy dissipation of anchored rock and energy absorption of bolt was established. Taking the coal-gangue separation system of Longgu coal mine as an example, the optimal anchoring angle can be determined as 57.5°–67.5°. Field monitoring showed fissured rock with the optimal anchoring angle, can not only effectively control the deformation, but also fully exert the energy-absorbing and efficiency-improving effect of bolt itself. This study provides guidance to the stability control and supporting design for deep engineering under the same or similar conditions.